By Andy Sullivan
WASHINGTON, Aug 20 (Reuters) - Republicans counting on an unpopular president and a favorable electoral landscape to help them win control of the U.S. Senate could have another asset this year - stronger candidates who are less likely to say embarrassing things.
As the months-long primary season nears its end, Republican leaders appear to have achieved their goal of producing more disciplined Senate candidates who can avoid the kind of campaign blunders that cost the party winnable races in 2010 and 2012.
Candidates backed by the party's establishment and business allies secured Republican Senate nominations in states like North Carolina, Colorado and Arkansas that will be hotly contested in November, in some cases beating out rivals backed by the insurgent Tea Party movement.
Tea Party challengers also failed to unseat any of the 12 sitting Republican senators who are up for re-election.
The Republican establishment celebrated another victory on Tuesday when their preferred candidate, former Alaska Attorney General Dan Sullivan, won the nomination to oppose Democratic Senator Mark Begich. Sullivan beat two other contenders, including one endorsed by home-state Tea Party hero Sarah Palin.
The results have left Republicans upbeat about their prospects in the Nov. 4 elections, when they need to pick up six seats from Democrats to win control of the 100-seat chamber.
"It's the best recruiting class in decades," said Rob Engstrom of the U.S. Chamber of Commerce, which has spent at least $15 million to back business-friendly candidates this cycle.
Many forecasters now give Republicans a slightly better-than-even chance of winning control of the Senate. They are heavily favored to pick up open Democratic seats in South Dakota, Montana and West Virginia, and six other competitive races will be fought in conservative-leaning states that President Barack Obama lost when he ran for re-election in 2012.
Obama isn't likely to be much help for Democrats. His approval ratings have not topped 50 percent since early 2013, and vulnerable incumbents like Colorado Senator Mark Udall have been avoiding him on the campaign trail.
But a favorable political environment is no guarantee of success, as Republicans have found in recent elections.
"One of the things we heard after 2012 is candidate quality matters," said Brad Dayspring, communications director of the National Republican Senatorial Committee, which ran a "candidate school" for hopefuls to bring them up to speed on policy issues and anticipated Democratic lines of attack.
That's a contrast to 2010 and 2012, when undisciplined candidates doomed the party's chances of winning the Senate. Republican candidate Christine O'Donnell lost the Delaware Senate race in 2010 after proclaiming she was "not a witch."
In 2012, Todd Akin lost Missouri after asserting victims of "legitimate rape" had the ability to block a pregnancy. Richard Mourdock saw his lead wither away in Indiana after saying a pregnancy resulting from rape was something "God intended to happen."
Those comments also hurt Republicans in other races, as Democrats used them to argue the party was out of touch with mainstream voters.
"One thing Democrats were really good at was taking the Todd Akins and Richard Mourdocks and Christine O'Donnells of the world and using them to infect other Senate campaigns," said Jennifer Duffy, an analyst with the nonpartisan Cook Political Report.
This year, Republican Senate candidates with a flair for controversy won't be on the ballot in November.
U.S. Representative Paul Broun, who called biological evolution and the Big Bang theory "lies straight from the pit of Hell" finished a distant fourth in the Georgia Senate primary in May. Milton Wolf, a radiologist who joked about gunshot victims on Facebook, fell short in his bid to unseat Kansas Senator Pat Roberts earlier this month.
Chris McDaniel, a Tea Party favorite who made sexually suggestive comments about Hispanic women on a radio show, narrowly lost a challenge to Mississippi Senator Thad Cochran.
Meanwhile, Democrats have been playing defense in Iowa after their nominee Bruce Braley drew negative attention for threatening to sue a neighbor over unfenced chickens and disparaging the farm state's senior senator, Republican Charles Grassley, as a "farmer from Iowa who never went to law school."
Democrats say Senate candidates backed by the Republican establishment are no sure bet, having lost in recent years in Montana, North Dakota, Wisconsin and Virginia.
This year, Republicans like Tom Cotton in Arkansas and Corey Gardner in Colorado will have to explain their votes in the House of Representatives on contraception, farm policy and other issues that could alienate a statewide electorate, said Matt Canter of the Democratic Senatorial Campaign Committee.
"What makes a candidate loved by the Republican establishment is sometimes the thing that makes them detested by voters," Canter said.
Still, Republicans like their chances.
"At the end of the day, this all comes down to product. The product out there, the candidates, are of much stronger caliber than in previous election cycles," said Paul Lindsay, spokesman for American Crossroads, a Republican "Super PAC" that has spent at least $5.7 million in political races so far this year.
(Reporting by Andy Sullivan; Editing by John Whitesides and Cynthia Osterman)